Method to divide upstream timeslots in a time division multiple access system, related line terminator and related network terminator

ABSTRACT

A method to divide upstream timeslots in a multiple access system that couples a line terminator (LT) via a tree-like network to a plurality of network terminators (NT 1 , NT 2 , . . . , NT 16 ) and that distributes downstream data packets by the line terminator to the plurality of network terminators. The method includes the following steps:  
     inclusion by the line terminator in a downstream data packet at a predefined place of a grant (TEA 1 ; TEA 2 ; . . . ; TEA 16 ) being associated to one of the plurality of network terminators and distributing that downstream packet,  
     reacting by the network terminator upon reception and recognition of its own grant by transmitting an upstream data packet in a predefined upstream timeslot.  
     In the event when the network terminator is a lower order network terminator and the predefined place is a predefined first place, the upstream data packet are transmitted in a lower order timeslot.  
     In the event when the network terminator is a higher order network terminator and the predefined place is a predefined first place, the upstream data packet is transmitted in one of a plurality of higher order timeslots, where the higher order timeslots are subslots of a predefined number of higher order subslots included in the predefined upstream timeslot.  
     In the event when the network terminator is a higher order network terminator and the predefined place is a predefined second place, the upstream data packet is also transmitted in such higher order timeslot.

[0001] The present invention relates to a method to divide upstreamtimeslots in a time division multiple access system as specified in thenoncharacteristic part of claim 1 and to a related line terminator and arelated network terminator as specified in the characteristic parts ofclaims 2 and 3.

[0002] Such a method and the related network and line terminators arealready known in the art, e.g. from the “ITU-T Recommendation G.983.1(10/98) section 8.3.5”. Therein, it is explained how grants should beincluded in Physical Layer Operation and Maintenance (PLOAM) cells forsending from a line terminator in a Passive Optical Network (PON) systemto a plurality of network terminators of the system to indicate to thenetwork terminators what upstream time slot they can use fortransmission of data to the line terminator. The systems described inthe recommendation are more specifically 155/155 Mbit/sec and622(downstream)/155 Mbit/sec systems wherein upon detection of itsidentity in a received grant, a network terminator can use a 155 Mbit/sframe to send upstream data.

[0003] In order to support higher rates upstream, the same principle asdescribed above could be used, i.e. sequential allocation of grants inthe PLOAM cells to allow network terminators to use f.i. 622 Mbit/secupstream timeslots. However, such a system would not be compatible witha 622/155 Mbit/sec system since the frame structures would not map.

[0004] An object of the present invention is therefore to provide amethod and a related line terminator and network terminator of the aboveknown type but which would allow graceful upgrade of the existingsystems to higher upstream speeds.

[0005] According to the invention, this object is achieved by means of amethod, a line terminator and a network terminator according to claim 1,2 and 3 respectively wherein network terminators transmitting at higherspeed, e.g. 622 Mbit/sec are called higher order network terminators andnetwork terminators sending at lower upstream speed, e.g. 155 Mbit/sec,are called lower order network terminators.

[0006] Indeed, by, in case of higher order network terminators, using inaddition to the normally available grants, i.e. grants located at apredefined first place, called non-idle grants in the aboveRecommendation, additional grants, i.e. grants located at a predefinedsecond place, in the above Recommendation called idle grants, and byadequately subdividing the existing upstream timeslots in subslots,higher rates can be supported whilst still being able to support thelower order network terminators. E.g. in case of a combination of a622/155 Mbit/sec and a 622/622 Mbit/sec system, the network terminatorssending at the former speed will upon receipt of a grant located at thepredefined first place (non-idle grant place) use the complete 155Mbit/sec upstream frame, whilst in the lafter system, the networkterminators upon receipt of a grant located either at a predefined firstor at a predefined second place (idle grant place) will use a subframebeing ¼th of the 155 Mbit/sec one.

[0007] Upstream frames used by lower order network terminators arecalled lower order timeslots, whilst slots used by a higher ordernetwork terminator are called higher order timeslots, these slots beingin fact subslots of the upstream slots having the size of lower ordertimeslots.

[0008] It should further be noticed that the term “including”, used inthe claims, should not be interpreted as being limitative to the meanslisted thereafter. Thus, the scope of the expression “a device includingmeans A and B” should not be limited to devices consisting only ofcomponents A and B. It means that with respect to the present invention,the only relevant components of the device are A and B.

[0009] The above and other objects and features of the invention willbecome more apparent and the invention itself will be best understood byreferring to the following description of an embodiment taken inconjunction with the accompanying drawings wherein:

[0010]FIG. 1 shows a block scheme of an embodiment of a time divisionmultiple access network wherein the method of the invention is used;

[0011]FIG. 2 shows a downstream frame format and an upstream frameformat used by the time division multiple access network of FIG. 1.

[0012] Referring to FIG. 1 a method to divide upstream timeslots used ina time division multiple access network in order to support 622/155Mbit/sec as well as 622/622 Mbit/sec will be described. The working ofthe time division multiple access network will be explained by means ofa functional description of the blocks shown in FIG. 1. Based on thisdescription, implementation of the functional blocks in FIG. 1 will beobvious to a person skilled in the art and will therefor not bedescribed in detail.

[0013] The time division multiple access network includes a lineterminator LT and a plurality of network terminators NT1, NT2, NT3, . .. , NT15, NT16. The line terminator LT is coupled to each networkterminator NT1, NT2, NT3, . . . , 257 NT15, NT16 via the cascadeconnection of a common transmission link Lc and an individual user linkL1, L2, L3, . . . , L15, L16.

[0014] The time division multiple access network is an optical networktransporting f.i. asynchronous transfer mode ATM cells over opticalfibers from the line terminator LT to the network terminators NT1, NT2,NT3, . . . , NT15, NT16. The time division multiple access networkbroadcasts network terminator identities e.g. TEA1, TEA12, TEA16, TEA3,TEA7, . . . or grants in downstream information packets form the lineterminator LS to the plurality by network terminators NT1, NT2, NT3, . .. , NT15, NT16. Upon detection of its own identity a network terminatoris allowed to transfer a predetermined amount of upstream informationpackets in predetermined upstream timeslots to the line terminator LT.For example: upon detection of network terminator NT3 of its ownidentity TEA3, network terminator NT3 is allowed to send to the lineterminator upstream information packets in predetermined timeslots.

[0015] The line terminator LT includes a packet formatting module PFM,inclusion means INC and queuing means Q. The queuing means Q is coupledto the inclusion means INC which is included following this embodimentin the packet formatting module PFM.

[0016] Each network terminator, whereof only network terminator NT3 isshown in detail in order not to overload the figure, includesrecognition means REC and transmitting means TR.

[0017] The functions of each functional blocks of above will bedescribed in the following paragraphs.

[0018] The line terminator allocates the time slots in a flexible anddynamically way. Indeed the upstream transfer capacity of the timedivision multiple access network is shared amongst the networkterminators NT1, NT2, NT3, . . . , NT15, NT16 based on their needed andrequested upstream bandwidth to transmit upstream information. Thisneeded upstream bandwidth is requested by the network terminators NT1,NT2, NT3, . . . , NT15, NT16 to the line terminator LT. The requestedbandwidth is translated by the line terminator LT in a predeterminednumber of allocated timeslots. This is realized by creating accordingthe requested bandwidth of the network terminators NT1, NT2, NT3, . . ., NT15, NTS16 a stream of transmit enable addresses or grants which arecalled in this application substation identities TEA1, TEA12, TEA16,TEA3, TEA7, . . . and which correspond to the grants as specified inITU-T Recommendation G.983.1. It has to be remarked that the detailedworking of this allocation goes beyond the scope of this invention andis therefore not described. A detailed description of this working canbe found in the published European patent application with publicationnumber 0 544 975. The aim is the use of the stream of substationidentities or grants TEA1, TEA12, TEA16, TEA3, TEA7, . . . to inform thenetwork terminators NT1, NT2, NT3, . . . , NT15, NT16 of the allocatedtimeslots. Following this embodiment the stream of substation identitiesor grants TEA1, TEA12, TEA16, TEA3, TEA7, . . . is provided to theinclusion means INC by the queuing means Q.

[0019] Physical Layer Operation and Maintenance cells, shortly PLOAMcells, are also provided to the inclusion means INC. The inclusion meansINC inserts in the PLOAM cells the grants and the PLOAM cells are thenincluded in the downstream information packets. In order to explain thesubject method, it is supposed that network terminator NT2 is a lowerorder network terminator, i.e. a network terminator sending at 155Mbit/sec, whilst network terminator NT3 is a higher order networkterminator sending at 622 Mbit/sec and that the downstream speed is 622Mbit/sec.

[0020] Referring to FIG. 2 the downstream frame format and the upstreamframe format used by the time division multiple access network of FIG. 1is shown. As it can be seen on FIG. 2, after 27 ATM cells a PLOAM cellis inserted.

[0021] NT2 being a lower order network terminator, the inclusion meansINC inserts a grant TEA2 for this terminator in PLOAM 1 or PLOAM 2 atthe location of non-idle grants as specified in ITU-T RecommendationG.983.1, version 10/98 on pages 39 and 41. It is supposed here as shownin FIG. 2 that at a chosen point in time a grant for NT2 is included inPLOAM1. Grants for NT3 which is a higher order network terminator areincluded at the place of non-idle grants and of idle grants. It issupposed here that grants are inserted in PLOAMS 1 and 3. How manygrants are included depends as mentioned earlier on the bandwidthrequested by the network terminators. The queuing means Q provides thegrants to be included to the including means INC in a sequence whichdepends on the allocated bandwidth. Since the way in which the numberand sequence of allocated grants is determined is outside of the scopeof the current invention, this is not explained in detail. Examples ofhow this is done can be found in the earlier mentioned patentapplication and in EPA 0854659.

[0022] The PLOAM cell after inclusion of the network terminator grantsis shown in FIG. 1 as PLOAM′. The PLOAM cell is packed by the packetformatting module PFM into the downstream frame format and distributedto the plurality of network terminators. A network terminator has todetect its own identity in a received PLOAM cell in order to be allowedto transfer an upstream information packet. This is realized by thedetecting means DET. The sending of the upstream information packets isdone by the transmitting means TR. In order not to overload FIG. 1 onlyfor network terminator NT3 the detecting means DET(TEA3) and thetransmitting means (TR) is shown. Taking as example the downstream frameof FIG. 2, NT2 first recognises its identity in a non-idle grantlocation of PLOAM1, and being a lower order network terminator, it thentransfers an information packet in a 155 Mbit/sec timeslot. Thesubsequent identity transferred by the line terminator is that of NT3,also in PLOAM 1. Upon detection of its own identity and knowing that itis an higher order network terminator, NT3 is allowed to transfer anupstream information packet in a subslot of an 155 Mbit/sec slot being¼th thereof. In order not to have gaps in the upstream frames, the lineterminator has included a subsequent grant for NT3 in PLOAM3 at thelocation of an idle grant. Upon detection of its identity, NT3 sends anupstream information packet in a subsequent subslot as shown in FIG. 2.In this way, NT3 is enabled to send upstream information packets at 322Mbit/s, whilst NT2 sends at 155 Mbit/s, and only one frame format isused which is suited for both speeds.

[0023] It should be noted that although the above described network ofthe chosen embodiment is an asynchronous transfer mode ATM network theapplication of the present invention is not restricted to the field ofATM. Small modifications, evident to a person skilled in the art may beapplied to the above described embodiment to adapt it to be method todivide upstream timeslots integrated in other time division multipleaccess networks wherein physical layer operation and maintenance partsare predefined in downstream information packets.

[0024] While the principles of the invention have been described abovein connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation on the scope of the invention, as defined in the appendedclaims.

1. Method to divide upstream timeslots in a multiple access system that couples a line terminator (LT) via a tree-like network to a plurality of network terminators (NT1, NT2, . . . , NT16) and that distributes downstream data packets by said line terminator (LT) to said plurality of network terminators (NT1, NT2, . . . , NT16), said method including the steps of: inclusion by said line terminator (LT) in a downstream data packet at a predefined place of a grant (TEA1, TEA2, . . . , TEA16) being associated to one of said plurality of network terminators (NT1, NT2 . . . , NT16) and distributing said downstream packet, and reacting by each one of said network terminators (NT1, NT2, . . . , NT16) upon reception and recognition of its own grant by transmitting an upstream data packet in a predefined upstream timeslot, characterised in that said step of transmitting includes, in the event when said one of said network terminators is a lower order network terminator and said predefined place is a predefined first place, transmitting said upstream data packet in a lower order timeslot, in the event when said one of said network terminators is a higher order network terminator and said predefined place is a predefined first place, transmitting said upstream data packet in one of a plurality of higher order timeslots, said higher order timeslots being subslots of a predefined number of higher order subslots included in said predefined upstream timeslot, and in the event when said one of said network terminators is a higher order network terminator and said predefined place is a predefined second place, transmitting said upstream data packet in a said higher order timeslot.
 2. A line terminator (LT) for realising division of upstream timeslots in a time division multiple access system that couples said line terminator (LT) via a tree-like network to a plurality of network terminators (NT1, NT2, . . . , NT16) and wherein said line terminator (LT) distributes downstream data packets to said plurality of network terminators (NT1, NT2, . . . , NT16) said line terminator (LT) comprising: inclusion means (INC) adapted to include in a downstream data packet at a predefined first place a grant (TEA1; TEA2; . . . ; TEA16) associated to one of said plurality of network terminators, characterized in that said inclusion means (INC) is further adapted in the event when one of said plurality of network terminators (NT3) is a higher order network terminator to include at a predefined second place of said downstream data packet a grant (TEA3) being associated to said one of said plurality of network terminators (TEA3).
 3. A network terminator (NT3) for use in a time division multiple access system that couples a line terminator (LT) via a tree-like network to a plurality of network terminators (NT1, NT2, . . . , NT16) including said network terminator (NT3) said network terminator (NT3) comprising: recognition means (REC) to recognise its own grant (TEA3) in a downstream packet sent from said line terminator (LT) to said network terminator (NT3), and transmitting means (TR) to transmit a data packet in a predefined upstream timeslot upon recognition of said own grant (TEA3) characterised in that said network terminator (NT3) is adapted to transmit upstream data packets at a higher order data packet rate and that therefor said recognition means (REC) is further adapted to recognise its own grant (TEA3) at a predefined first place and that said transmitting means (TR) is adapted, upon recognition by said recognition means (REC) of said own grant (TEA3) at said predefined first place to transmit data packet in one of a plurality of higher order timeslots, said higher order timeslots being a subslot of a predefined number of higher order subslots included in said predefined upstream timeslot, and said recognition means (REC) being further adapted to recognise its own grant (TEA3) at a predefined second place and that said transmitting means (TR) is further adapted, upon recognition by said recognition means (REC) of said own grant (TEA3) at said predefined second place, to transmit said data packet in a said higher order timeslot.
 4. Method according to claim 1 , characterized in that said time division multiple access system is a Passive Optical Network (PON) system and that said downstream data packets are Physical Layer Operation and Maintenance (PLOAM) cells.
 5. Method according to claim 4 , characterized in that said first predetermined place is a location within said Physical Layer Operation and Maintenance (PLOAM) cells reserved for so-called non-idle grants as specified in the ITU-T Recommendation G.983.1, whereas said second predetermined place is a location within said Physical Layer Operation and Maintenance (PLOAM) cells reserved to idle grants as specified in the ITU-T Recommendation G.983.1. 